It is a Germination Inhibitor, it would prevent weed for seeding but if weed already there it wouldn't work. Now may be little late for may weeds like dandelion.
And it would inhibitor grass seeds too. You can't use it if you seed you lawn.
I still saw killex in Canadian Tire an walmart. So you still can buy them.
Went to both of Canadian Tire and Walmart (Kanata), didn't see any killex for sale. Only roundup. Where, and when did you see killex? Did you see it in store or website?